A typical wire stent for insertion and expansion in a collapsed or occluded blood vessel is shown in U.S. Pat. No. 4,800,882 and includes a coiled wire having a plurality of curved sections that are formed into a generally circular configuration. Adjacent curved sections are joined by a bend so that a series of alternating opposing loops are formed. The stent has a cylindrical shape with a longitudinal opening through which a folded balloon catheter is inserted. The opposing loops are tightly contracted about the catheter so that the cylindrical shape has an overlapping region in which portions of adjacent loops circumferentially overlap. The loops are arranged so that when the balloon catheter is inflated, adjacent loops diverge circumferentially relative to each other, thereby decreasing the width of the overlapping region while increasing the diameter of the cylindrical shape. As the diameter of the cylindrical stent increases, the stent engages the inner surface of the blood vessel.
In operation, the stent is deployed at its desired position within the vessel in its collapsed state, by threading the balloon catheter tip the vessel from an incision some distance away, and then expanded to its expanded state, for supportive engagement with the interior of the vessel wall.
The prior art stents have several deficiencies. As shown in FIG. 7 of U.S. Pat. No. 4,800,882, the alternating bends are aligned in relation to the longitudinal axis of the stent such that upon expansion of the stent as shown in FIG. 8, the opposing loops may be expanded such that a longitudinal gap appears between the opposing bends of the loops, leaving a longitudinal unsupported area along the occluded blood vessel. Such an unsupported area is undesirable. Further, when it is desired to support a branched section of a blood vessel without obstructing the passageway of the vessel, it is necessary to utilize several conventional stents to support the main vessel and the adjacent two branch vessels. Deployment of multiple stents requires an extended medical procedure, and may produce unsatisfactory results if any of the stents migrates away from the juncture, leaving one leg of the Y-shaped juncture of the vessels unsupported. Additionally, the stents of the prior art often require the application of heat, torsional force, or a shortening in length in order to attain their expanded state.
Alternatively, stents having no longitudinal gap may be comprise spiral coils, or other configurations that are radially expandable and provide the desired circumferential support for a collapsed vessel.
Because of the asymmetrical nature of many of the desired coil configurations, standard manufacturing methods are inapplicable. Thus, stents such as that disclosed in U.S. Pat. No. 4,800,882, involve a high degree of labor to produce. The present invention discloses means and apparatus for producing a desired stent quickly and easily.
The present invention overcomes the deficiencies of the prior art.